Induction of resistance and expression of defense-related genes in tobacco leaves infiltrated with Ralstonia solanacearum.

Ralstonia solanacearum 8107 (8107) is non-pathogenic to tobacco and elicits the hypersensitive response (HR). In Nicotiana tabacum cv. Samsun NN leaves infiltrated with 8107, acquired resistance to challenging tobacco mosaic virus (TMV) was induced 2-6 d after 8107-infiltration. hsr203J and hin1 genes were expressed only in the 8107-infiltrated area. On the other hand, the expression of PR-1a and PR-1b genes was not detected in the 8107-infiltrated area, but in areas other than that developing the HR. Expression of these PR-1 genes was regulated simultaneously and the kinetics of the expression was dependent on the distance from the infiltration area. Therefore, diffusible signal(s) might be produced in HR-causing cells and transmitted to peripheral cells resulting in expression of PR genes. In NahG10 tobacco infiltrated with 8107, the HR was induced but resistance to TMV was not. Analysis using NahG10 tobacco also showed that the salicylic acid (SA)-dependent signal regulated the expression of hsr203J and PR-1a, but not that of hin1 and PR-1b. These results suggest that resistance of tobacco to 8107 is SA-independent and involves a quite different mechanism from acquired resistance to TMV induced by 8107-infiltration which is SA-dependent.